Esters and other carboxylic acid derivatives of 3,3,4,4-tetrahydroperfluoroalkylcarboxylic acids are made by the iron promoted reaction of an ester of bromodifluoroacetic acid or other carboxylic acid derivatives and a (perfluoroalkyl)ethylene.
The salts of 3,3,4,4-tetrahydroperfluoroalkylcarboxylic acids (THPA) are useful as surfactants in the polymerization of fluorinated olefins, for example tetrafluoroethylene, for example see U.S. Pat. No. 5,763,552. This patent describes a synthesis for these compounds by the copper catalyzed reaction of an ester of iododifluoroacetic acid with a (perfluoroalkyl)ethylene to form an iodo substituted ester of THPA, followed by reaction with a tin hydride to form a THPA ester. This 2 step synthesis, which apparently gives 50-60% overall yields of the ester, involves the use of expensive tin hydrides, which also pose a disposal problem. The THPA ester is then hydrolyzed to the THPA, and converted to a salt by reaction with base. The salt is useful as a surfactant in fluoroolefin polymerizations.
C-M Hu et al., J. Chem. Soc., Chem. Commun., 1993, p. 72-73 report the synthesis of 3-bromodifluoromethyl substituted propanoic acids and esters by the iron and CrCl3 promoted reaction of dibromodifluoromethane with various substituted and unsubstituted acrylic acids and esters. No mention is made of using (perfluoroalkyl)ethylenes as reactants.
This invention concerns a process for the production of 3,3,4,4-tetrahydroperfluoroalkanoates, comprising, contacting at about 25xc2x0 C. to about 150xc2x0 C. in a liquid medium, iron, a first compound of the formula R1CHxe2x95x90CH2, and a second compound of the formula Br(R2)CFY wherein:
R1 is perfluoroalkyl containing 1 to 30 carbon atoms;
R2 is fluorine or perfluoroalkyl;
Y is xe2x80x94CN, CO2H, xe2x80x94CO2R3, or xe2x80x94C(O)NR42;
R3 is hydrocarbyl or substituted hydrocarbyl; and
each R4 is independently hydrogen, hydrocarbyl or substituted hydrocarbyl.
By hydrocarbyl is meant a univalent radical containing only carbon and hydrogen. By substituted hydrocarbyl herein is meant a hydrocarbyl group that contains one or more (types of) substituents that does not interfere with the operation of the polymerization catalyst system. Suitable substituents in some polymerizations may include some or all of halo, ester, keto (oxo), amino, imino, carboxyl, phosphite, phosphonite, phosphine, phosphinite, thioether, amide, nitrile, and ether. Preferred substituents are halo, ester, amino, imino, carboxyl, phosphite, phosphonite, phosphine, phosphinite, thioether, and amide.
Herein by a 3,3,4,4-tetrahydroperfluoroalkanoate is meant a compound of the formula R1CH2CH2CR2FY, wherein R1, R2 and Y are as defined above. In preferred first compounds R1 is n-perfluoroalkyl containing 1 to 10 carbon atoms. In preferred second compounds:
R2 is perfluoro-n-alkyl containing 1 to 10 carbon atoms or fluorine, especially R2 is fluorine; and/or
Y is xe2x80x94CO2H or xe2x80x94CO2R3 wherein R3 is alkyl, and especially preferably R3 is alkyl containing 1 to 6 carbon atoms.
By a liquid medium is meant a liquid in which the first compound and the second compound are soluble. By soluble in this context is meant that at least 1 weight percent, preferably at least 5 weight percent, of each of the first and second compound will dissolve in the liquid at 30xc2x0 C. Useful liquid media are organic liquids, particularly more polar organic liquids such as alcohols, ethers, ketones, etc. Preferred materials for the liquid medium are aliphatic alcohols containing 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms, and especially preferably methanol or ethanol. When an alcohol is used as the liquid medium, if Y is xe2x80x94CO2H or xe2x80x94CO2R3, and R3 is not the same as the alkyl group of the alcohol, the resulting R3 in the product may be the alkyl group of the alcohol. In other words esterification or transesterification may take place. For example if Y is xe2x80x94CO2R3, and R3 is ethyl, and the liquid medium is methanol, R3 in the product may be (mostly) methyl.
The iron (metal) present in the reaction need not be in any particular form, but it is preferred that it have a relatively high surface area, for example be in the form of iron powder or so-called iron filings. However the source of the iron can even be the reactor vessel, for example steel or another iron alloy.
If desired CrCl3 may also be present in the reaction, although it is preferred that it not be present.
The molar ratio of the ingredients is not critical, but typically a molar excess of the first compound over the second compound will be present, and a molar excess of iron over the first compound will also be present. This usually makes the most efficient use of the normally most expensive compound, the second compound. The concentrations of the reactants in the liquid medium are not critical, typical concentrations being illustrated in the Examples.
The time of reaction is not critical, a period of time sufficient to achieve the desired conversion at the temperature used being useful. Typical reaction times are 1 to 100 hours, more typically 3 to 50 hours. The process is run at about 30xc2x0 C. to about 150xc2x0 C., preferably about 50xc2x0 C. to about 100xc2x0 C. The pressure at which the process is run is also not critical, atmospheric pressure being convenient. In the case of running the process at temperatures above the boiling point(s) of one or more of the ingredients, it may be useful to run the process in a pressure vessel at autogenous pressure.
No matter what Y is in the first compound, it may be converted to a carboxyl group (if it is not already a carboxyl group) by hydrolysis using standard organic chemical techniques, see for instance U.S. Pat. No. 5,763,552, which is hereby included by reference. The carboxyl group may then be converted to a salt, preferably an ammonium or alkali metal salt, which is then may be used as a surfactant in a fluoroolefin free radical polymerization, again see U.S. Pat. No. 5,763,552.
In the Examples pressures are gauge pressures, except where noted. In the Examples the following abbreviations are used:
Etxe2x80x94ethyl
EtOHxe2x80x94ethanol
GC-MSxe2x80x94coupled gas chromatography-mass spectroscopy
Mexe2x80x94methyl
MeOHxe2x80x94methanol
i-PrOHxe2x80x94isopropanol
PrOHxe2x80x94n-propanol
PFBExe2x80x94(perfluorobutyl)ethylene
Prxe2x80x94propyl
i-Prxe2x80x94isopropyl
PFBE was obtained from E. I. du Pont de Nemours and Company, Wilmington, Del., U.S.A., iron powder was obtained from Aldrich Chemical Co., Milwaukee, Wis., U.S.A., and ethyl bromodifluoroacetate was obtained from SynQuest Lab., Inc., Alachua, Fla., U.S.A.